The present invention relates to feed structures for antennae, and more particularly to a waveguide feed structure and reflector antennae using same.
FIG. 1A illustrates a conventional reflector antenna 100 having a waveguide feed 120 which uses a waveguide bend 130 to feed the reflector 140 at the focal point of the reflector.
FIG. 1B illustrates conventional E- and H-plane radiation patterns for the waveguide feed 120. A typical radiation pattern for the antenna 100 is defined as the range over which the antenna 100 provides a gain of −10 dB relative to a 0 dB signal at the antenna boresight. This selection is weighted by the balance of aperture efficiency and the spill over loss. Referring to the radiation patterns of FIG. 1B, the energy of the antenna feed from ±53° (total 106°) intersects the reflector 140, but the energy from 53-180° is lost in space, such loss referred to as “spill over loss,” as known in the art, such loss reducing the antenna's efficiency, or effective collection area. Moverover, the spill over loss generates unwanted sidelobes which can further interfere with the desired transmission/reception of the intended signal.
FIG. 2 illustrates an improved reflector antenna 200 operable to attenuate unwanted sidelobes. The improved antenna 200 includes the waveguide feed 120 the waveguide bend 130 and the reflector 140 described above, these components enclosed within a housing formed by a signal-transparent radome 220 and absorbing walls 230 located on the periphery of the reflector 140 which operate to attenuate the spill over energy to decrease the generation of sidelobes. While the sidelobe rejection of this antenna is improved, the resulting structure is large and heavy, and may not be suitable in particular environments, e.g., in high wind environments.
FIG. 3 illustrates another improved reflector antenna as disclosed in U.S. Pat. No. 7,075,492 which also has improved sidelobe rejection and does not require the absorber sidewalls as the prior art antenna of FIG. 2. This antenna employs a waveguide feed 320 which operates to illuminate a deep contour reflector over a wide radiation pattern range of ±97° (total 194°). The improved reflector antenna 300 is small and light weight, however the antenna exhibits a relatively large taper/roll off in its aperture field distribution, e.g., 14-20 dB roll off between a signal on boresight versus a signal at the reflector's edge. As a consequence, the antenna 300 has a low aperture efficiency.
What is therefore needed, is an improved waveguide antenna feed and antenna assembly which provides advantages over the aforementioned.